Anti-Microbial Fibres and Their Production

ABSTRACT

Anti-microbial lyocell fibres incorporate an anti-microbial composition which comprises a silver compound deposited on a support material in the form of porous particles having an extended surface area and comprising an oxidic material which is essentially insoluble in water and incapable of forming hydrates. A preferred composition is silver chloride on titanium dioxide particles. The anti-microbial effect is durable to processing and the fibres are not adversely discoloured. Low concentrations of the anti-microbial composition of below 0.1 percent by weight on weight of cellulose may be used. In the process of making the fibres, the anti-microbial composition preferably is added to the pasty pre-mix of the spinning solution.

FIELD OF THE INVENTION

The present invention relates to anti-microbial lyocell fibres which canimpart qualities of freshness and hygiene to fabrics made from thefibres. It also relates to a process for making such fibres.

BACKGROUND ART

There is an increasing interest in fabrics offering qualities ofimproved hygiene and freshness, for example for use as clothing, andalso in fabrics having better protection from deterioration caused bymicrobes.

One way of achieving this is to apply anti-microbial agents to thefabric, for example as a finishing treatment. Another way, offeringgreater commercial flexibility, is to provide fibres that are alreadyanti-microbial, by virtue of having an anti-microbial agent applied toor incorporated into the fibres.

Many organic anti-microbial agents have been used or proposed for use onfibres, including triclosan, biguanides, phenols and derivatives,isothiazolones, quaternary ammonium salts, tri-butyl tin oxide,haloamines and alcohols. The most widely used of these is triclosan,which has been used as a fibre finish and fabric finish for both naturaland man-made fibres and has also been incorporated into man-made fibressuch as regenerated cellulose fibres and acrylic fibres by inclusion inthe spinning dope. Inorganic anti-microbial agents have also been used,and these are predominantly compounds in which a metal ion such assilver is supported on an inert matrix. An example of such an agent issilver zeolite.

Lyocell fibres are produced by extrusion of a solution of cellulosethrough a spinning jet into a coagulation bath by a process known assolvent spinning. They are therefore alternatively known as solvent-spuncellulose fibres. Such a process is described in U.S. Pat. No. 4,246,221and uses as the solvent an aqueous tertiary amine N-oxide, particularlyN-methylmorpholine N-oxide. Lyocell fibres are distinguished fromregenerated cellulose fibres, such as viscose fibres, which are producedby forming the cellulose into a soluble chemical derivative and thenextruding a solution of this derivative into a bath, which regeneratesthe extrudate as cellulose fibres.

Unfortunately, many of the anti-microbial agents that can beincorporated into other man-made fibres are incompatible with the amineoxide spinning system used to make lyocell fibres. For example,triclosan is too easily washed out of the fibres during processing.Also, some silver ion complexes are deactivated by amine oxide solventsand yield a brown or yellow colouration on the fibres that is notacceptable. A process using silver ion complexes in cellulose fibres,including viscose rayon fibres and organic solvent-spun cellulosefibres, is described in JP-A-6-235116. The process described has notbecome commercial possibly because of compatibility problems and colourproblems with the spinning systems. Another process of this type isdescribed in EP-A-0 905 289 and involves adding to a solution ofcellulose in an amine oxide solvent a slurry of a silver-basedanti-bacterial agent and a magnetised mineral ore powder. The selectedsilver-based anti-bacterial agents include silver zeolites, silverzirconium phosphates and silver calcium phosphates. These silvercompounds produce unacceptable colour staining on the fibres.

Another concern with introducing silver compounds into the system formaking lyocell fibres arises from the fact that, in addition to theamine oxide solvent itself, the spinning solution and its precursorcomponents in practice also incorporate a stabiliser, particularlypropyl gallate. The purpose of this stabiliser is to sequester freeradicals, particularly metal ions, which can catalyse exothermicreactions in the system, leading to uncontrolled explosions. Use of sucha stabiliser is, therefore, believed to be universal in practice. Theconcern with adding silver compounds is twofold: firstly, that thestabiliser will sequester the silver, deplete it as residualanti-microbial agent and cause staining, and, secondly, that the silvercompound will use up the stabiliser and leave insufficient in the systemto protect against exothermic reactions.

WO 03/018166 and WO 2004/022822 also relate to cellulosic materialswhich may contain silver.

Anti-microbial compositions disclosed and claimed in EP-A-0251783, thecontents of which are hereby incorporated into this specification,comprise an anti-microbial silver compound deposited on a supportcomprising a physiologically inert oxidic synthetic material inparticulate form and having an extended surface area. These compositionswere developed by the proprietor of that patent, Johnson Matthey plc,for incorporation into coating or impregnating formulations for medicalor other appliances or for topical application to bandages anddressings. The present invention is concerned with the use ofanti-microbial compositions of this type.

DISCLOSURE OF THE INVENTION

The present invention provides anti-microbial lyocell fibresincorporating an anti-microbial composition which includes a silvercompound held on a support material, characterized in that theanti-microbial composition comprises a silver compound deposited on asupport material in the form of porous particles having an extendedsurface area and comprising an oxidic material which is essentiallyinsoluble in water and incapable of forming hydrates.

The support material, in the form of the porous particles, is oxidic andmay comprise an oxide or a hydroxide or a complex oxy-anion species suchas phosphate or sulphate. It is essentially insoluble in water and alsostable in water, in the sense of being incapable of forming a hydratebut being able to adsorb water to form an associated aqueous species.

Oxidic materials which may be used for the support material, used in theform of porous particles, include oxides of titanium, magnesium,aluminium, silicon, cerium, zirconium, hafnium, niobium and tantalum,calcium hydroxyapatite (a phosphate), and barium sulphate, all to theextent of being insoluble and stable in water as specified. Titaniumdioxide is a preferred oxidic support material and is stable to water inits anatase, rutfle and brookite crystalline forms; hydrated orhydratable oxides of titanium are not suitable for use in thisinvention.

The particle size of the porous particles which comprise the oxidicsupport material is preferably as small as possible commensurate withachieving the desired anti-microbial effect Preferably, the averageparticle diameter is less than about 25 microns and more preferably itis in the range 0.5 to 10 microns. The particles may have a highly openstructure, for example generally spherical clusters of crystalliteshaving a large physical voidage. The surface area of the particles mayextend from about 1 or 2 square metres per gram up to about 240 squaremetres per gram or more, but it is preferably in the range 5 to 100square metres per gram.

The silver compound deposited on the porous particles which comprise theoxidic support material is preferably one which has a low solubility inwater and aqueous media, for example a solubility below 0.01 gram perlitre of water at 20° C., and in which the silver is present as an ionicspecies. It may be present at a level of about 1 to about 75 percent byweight of the oxidic support material, preferably 10 to 60 percent byweight. A preferred silver compound is silver chloride. Silver phosphateis also suitable.

A preferred anti-microbial composition comprises silver chloridedeposited on titanium dioxide particles, with appropriate concentrationsof the silver chloride being, for example, about 15 to about 25 percent,such as about 15 percent, about 20 percent or about 25 percent, byweight based on the weight of the titanium dioxide particles.

The silver compound may be deposited on the porous support particles bycontrolled nucleation and growth so that the silver compound is largelycontained within the pores of the particles and the particle sizedistribution is maintained by avoiding any coalescence.

The anti-microbial composition may be used in relatively lowconcentrations in the lyocell fibres of the invention and still produceeffective anti-microbial properties. For example, with a compositioncomprising about 20 percent by weight of silver chloride deposited ontitanium dioxide particles, we have found that effective and durableanti-microbial properties are obtainable with concentrations of theanti-microbial composition in the fibres below about 1 per cent byweight owc (on weight of cellulose). In that circumstance, there is nobenefit in using higher concentrations as this would merely increase thecost and, depending on the level used, diminish the physical propertiesof the fibres. Indeed, much lower concentrations of that particularanti-microbial composition have been used satisfactorily, and it ispreferred to use a level of concentration below about 0.1 percent byweight owc. For example, good results have been achieved using aconcentration of 0.0125 percent by weight owc, which is a remarkably lowconcentration.

The fibres can, in addition to the silver-containing anti-microbialcomposition, contain a matting agent, for example Ti 0₂, to producefibres which are dull or matt. Matting agent concentrations of from 0.5to 2.5 percent by weight Ti 0₂ or equivalent can be used. Such agentsare especially useful for non-woven products.

The silver-containing fibres of the invention may be used in textilesfor hospital use (e.g. bedding, towels, gowns, uniforms), socks andunderwear, military textiles (combat suits), sportswear, interliningsfor garments and home textiles (mattresses and upholstery), fibre fillfor duvets pillows outdoor jackets and ski suits, blankets towels andtowelling, carpets and mats, and conveyor belts for frozen food, and fornon-wovens such as wound dressings (cosmetic pads, filters, wet wipes,wipes, baby wipes, medical devices, incontinence products, waterfilters, plaster cast linings, interlinings, roller towels, shoelinings, dry wipes and floor tiles.

The lyocell fibres may be carboxymethylated, partially or evencompletely.

The lyocell fibres of the invention possess excellent anti-microbialproperties, and these properties are durable to conventional scouring,washing and dyeing procedures for lyocell fibres and fabrics. The fibresretain their usual good mechanical properties and are not spoiled bycolour staining or by permanent yellowing or greying. To the extent thatthere is a slight fall in whiteness of the fibres, this is onlytemporary and is removed by the normal washing and scouring processes towhich the fibres are subjected in manufacture.

Considering the previous experience with trying to use silver-basedanti-microbial compositions in lyocell fibre manufacture, the propertiesof the lyocell fibres of the invention are both excellent andunpredicted.

The invention includes a process for making anti-microbial lyocellfibres in which cellulose is dissolved in a solvent of aqueous amineoxide to form a spinning solution which is extruded through a spinningjet into a coagulation bath to produce lyocell fibres, and ananti-microbial composition is incorporated into the fibres,characterized in that the anti-microbial composition is added to thefibre spinning solution or to a precursor or ingredient of that solutionand comprises a silver compound deposited on a support material in theform of porous particles having an extended surface area and comprisingan oxidic material which is essentially insoluble in water and incapableof forming hydrates.

The anti-microbial composition may be added to the spinning solution orto an ingredient of that solution, for example the amine oxide solvent.However, it is preferably added to a precursor of the cellulose solutioncomprising a pasty pre-mix of the cellulose pulp and the amine oxidesolvent. One method of forming the solution of cellulose in an amineoxide solvent such as tertiary amine N-oxide, for exampleN-methylmorpholine N-oxide, is to form a pre-mix of cellulose andaqueous amine oxide solvent incorporating an excess of water over theoptimum required for solution to take place. The pre-mix, which is apaste or dough, is then subjected to an evaporation process, for examplein a thin-film evaporator, to remove the excess water and form asolution of the cellulose. The anti-microbial composition, which hasbeen added to the pre-mix, is effectively dispersed throughout thisresulting cellulose solution.

In this preferred solution process, the anti-microbial composition maybe added to the pre-mix itself or to an ingredient of the pre-mix,preferably the former.

The anti-microbial composition may be added in the form of a dispersionin a liquid, for example in water, or in dry powder form. It may beadded to the vessel in which the pre-mix is made but, preferably, isadded to the pre-mix in the hopper feeding the pre-mix to the thin filmevaporator which forms the spinning solution. Addition may be made usinginjection equipment such as is used to add matting agents such astitanium dioxide. In fact, the anti-microbial composition and thematting grade of titanium dioxide may be added together.

The process of the invention may be carried out without any significantprocessing problems. The sequestering stabiliser, which is preferablypropyl gallate, appears to remove insignificant amounts of the silvercompound from the anti-microbial composition. The oxidic supportmaterial appears to stabilise the silver compound against the activityof the propyl gallate during the manufacturing process. The corollary ofthis is that the propyl gallate does not become excessively used up byreacting with the silver compound and instead remains in the system toscavenge radicals which could otherwise trigger explosive exothermicreactions. Propyl gallate does not leave the spinning system with thefibres and so cannot affect the anti-microbial composition once it isincorporated into the fibres.

There may be a slight fall in whiteness of the spun fibres compared withstandard lyocell fibres, but this is only temporary. Normal standards ofwhiteness are restored by the usual washing and scouring steps to whichthe spun lyocell fibres are subjected. It is thought that any colourpresent is a complex formed between a chromophore of degraded amineoxide together with the propyl gallate and the silver compound. Thiscomplex does not appear to become bound to the cellulose of the lyocellfibres.

The invention is illustrated by the following Examples:

EXAMPLES 1 & 2

The anti-microbial composition used for the purposes of both of theseExamples was a product, JMAC-PG, supplied by AddMaster (UK) Ltd. andcomprised a dry powder of porous titanium dioxide particles on which 20percent by weight of silver chloride had been deposited. The particlediameters were in the range 0.5 to 2 microns, with the majority ofparticles being sub-micron in diameter.

The fibre-making process was based on a commercial process for makinglyocell fibres of 1.4 dtex by spinning a solution of cellulose in asolvent of aqueous N-methylmorpholine N-oxide through a spinning jetinto an aqueous coagulating bath to form fibres.

The spinning solution was made by a process in which cellulose pulp andthe solvent of aqueous N-methylmorpholine N-oxide were fed into a mixingvessel and mixed to form a paste or dough, known as the pre-mix. Thesolvent contained excess water over the optimum required for thecellulose to go into solution, in order to promote efficient wetting andmixing of the cellulose with the solvent. This excess water was thenevaporated from the pasty pre-mix by passing the pre-mix through a typeof thin-film evaporator called a Filmtruder (trademark of BUSS AG) toform the spinning solution.

The JMAC powder was dispersed in water and added as a dispersion to thepre-mix at the hopper feeding the pre-mix into the Filmtruder. Twodifferent concentrations of JMAC were used in two different productionruns. The first (Example 1) was a concentration of 125 ppm (parts permillion) by weight owc, which is 0.0125 percent by weight owc. Thesecond (Example 2) was a concentration of 250 ppm by weight owc, whichis 0.0250 percent by weight owc.

The JMAC anti-microbial composition was evenly distributed in thespinning solution formed by the Filmtruder and so was evenly distributedin the spun lyocell fibres. The JMAC composition did not adverselyaffect the process of making the spinning solution or of spinning thefibres, and it was not itself adversely affected by these processes.

The fibres were tested for physical properties and found to haveproperties generally in line with a Control fibre, which was a standardTencel lyocell fibre of 1.4 dtex. (Tencel is a registered trademark ofLenzing Fibers Limited.)

The results of the physical property measurements are shown below inTable 1: TABLE 1 Example 1 Example 2 Control (125 ppm (250 ppm SampleFibre JMAC) JMAC) Dry breaking tenacity (cN/tex) 33.1 34.0 36.3 Drybreaking extension (%) 11.3 11.8 11.8 Dry initial modulus 1250 1272 1440Knot breaking tenacity (cN/tex) 22.4 20.2 21.1 Knot extension at peak(%) 14.9 10.3 11.8 Loop breaking tenacity (halved) 13.9 13.9 12.1(cN/tex) Loop extension at peak (%) 2.8 2.6 1.8

Samples of spun yarns of count 20 Tex were made from the respectivefibres of Examples 1 and 2 and of the Control, the fibres having beencut to 38 mm staple length. These yarns were used to weave respectivegreige fabrics in an interlock construction, each of basis weight 200gms per square metre.

A portion of each of the fabrics made from the respective fibres of theExamples and of the Control was given a scour in an aqueous scour bathcontaining 2 g/l (gms per litre) of soda ash and 2 g/l Zetex HPLFN for30 minutes at a temperature of 70° C.

The scoured fabrics produced from the fibres of Examples 1 & 2 weretested for colour whiteness against the scoured Control fabric producedfrom the standard lyocell Control fibres. Testing was carried out usinga Minolta Spectrophotometer CM-3300d and produced a CIE (CommissionInternationale d'Eclairage) whiteness index of 70.7 for the fabric ofExample 1 and a CIE whiteness index of 67.1 for the fabric of Example 2,as against a CIE whiteness index of 73.7 for the Control fabric. Thisshows that the anti-microbial composition JMAC has no significant effecton fibre colour, particularly at the lower concentration of 125 ppm usedin Example 1.

The fabrics were re-tested after controlled exposure to a xenon lamp,which mimicked 4 weeks' outdoor natural light exposure, and, again,there was little difference in colour between the fabrics.

Anti-microbial testing of the fibres of Examples 1 & 2 was carried outusing two different tests:

Qualitative Agar Plate Test (Swiss SNV 195-920)

This is a quick test to determine the anti-microbial activity ofleaching anti-microbial agents on a sample of fibre. Evaluation is basedupon the presence or absence of bacterial growth beneath and surroundingthe sample (inhibition zone). Non-leaching anti-microbial agents show nozones of inhibition and weak bacterial growth beneath the samples.

This test was carried out using a Staphylococcus aureus bacterium.

The results showed that each of the fibre samples of Examples 1 & 2produced no zones of inhibition and weak bacterial growth beneath thesamples, which confirmed the anti-microbial composition JMAC as being ofthe non-leaching type. This is the preferred type of agent foranti-microbial fibres because one is looking for a prolonged effect inwhich the agent acts at the fibre boundary but does not leach beyond it,for example onto skin adjacent to clothing.

Quantitative Dynamic Shake Flask Test (ASTM E2149-01)

This is a test of the American Society for Testing and Materials, whichmeasure the anti-microbial activity of both leaching and non-leachinganti-microbial materials under dynamic contact conditions.

Evaluation is based upon the calculated percentage reduction in bacteriafrom counts taken at various times and expressed as calculatedpercentage reduction and also as log reduction versus a no-samplecontrol.

The fibres of each of Examples 1 & 2 were tested alongside Controlfibres, and also against a control in which no fibres were used, i.e. ano-sample control. Three different bacteria were tested: theStaphylococcus aureus bacterium; the Klebsiella pneumoniae bacterium;and the methicillin-resistant Staphylococcus aureus bacterium (MRSA).

Samples of the respective fibres were also tested after being given oneor more of the following treatments:

-   -   1. A scour in an aqueous scour bath containing 2 g/l of soda ash        and 2 g/l Zetex HPLFN for 30 minutes at a temperature of 70° C.    -   2. Dyeing in an aqueous dyebath for 60 minutes at a temperature        of 80° C., the dyebath containing Procion Marine Blue H-EXL, a        reactive dye, at 2 percent by weight on weight of fabric and        soda ash at 20 g/l, followed by soaping off the dyed fabric.    -   3. A detergent wash in a washing machine for 120 minutes at a        water temperature of 60° C. using Persil Original Non-Biological        Automatic washing powder and Comfort fabric conditioner,        followed by tumble drying. (Persil and Comfort are trademarks of        Lever Faberge Limited).

The results for the dynamic shake flask tests on these fibres after 24hours are shown in the following Table 2. TABLE 2 StaphylococcusKlebsiella aureus pneumoniae MRSA Log Log Log % Reduc- % Reduc- % Reduc-Sample Kill tion Kill tion Kill tion Control 68.4 0.50 98.4 1.80 99.943.24 (scoured lyocell fibres) Example 1 99.94 3.24 99.99 4.25 99.9995.15 Example 2 99.94 3.24 99.99 4.25 99.999 5.15 Example 1 99.93 3.2099.99 4.20 99.999 5.15 (scoured) Example 2 99.93 3.20 99.99 4.20 99.9995.15 (scoured) Example 1 99.94 3.24 99.47 2.27 99.999 5.15 (scoured &dyed) Example 2 99.94 3.24 99.99 4.25 99.999 5.15 (scoured & dyed)Example 1 99.94 3.24 99.99 4.25 99.994 4.22 (scoured, dyed & washed)Example 2 99.94 3.24 99.98 3.75 99.999 5.15 (scoured, dyed & washed)

The results shown in Table 2 confirm strong anti-microbial activityagainst all three species of bacterium for the fibres of both Examples 1and 2. Furthermore, as shown, this strong activity is sustained afterthe scouring, dyeing and detergent washing treatments given and isconsidered durable. The anti-microbial results obtained for the fibresof Example 2 are, generally, no better than those obtained for thefibres of Example 1. Therefore, considerations of the better whitenessobtained with the fibres of Example 1 and the lower cost of using halfthe concentration of the JMAC anti-microbial composition, compared withthe fibres of Example 2, indicate that a concentration of 125 ppm byweight owc of the JMAC composition is to be preferred to higher amounts.

1. Anti-microbial lyocell fibres incorporating anti-microbialcomposition which includes a silver compound held on a support material,characterized in that the anti-microbial composition comprises a silvercompound deposited on a support material in the form of porous particleshaving an extended surface area and comprising an oxidic material whichis essentially insoluble in water and incapable of forming hydrates. 2.Anti-microbial lyocell fibres according to claim 1, characterized inthat the oxidic support material is selected from oxides of titanium,magnesium, aluminum, silicon, cerium, zirconium, hafnium, niobium andtantalum, calcium hydroxyapatite and barium sulphate.
 3. Anti-microbiallyocell fibres according to claim 1, characterized in that the oxidicsupport material is titanium dioxide in one or more of the crystallineforms anatase, rutile and brookite. 4-10. (canceled)
 11. A process formaking anti-microbial lyocell fibres by dissolving cellulose in asolvent of aqueous tertiary amine N-oxide to form a spinning solution,extruding the spinning solution through a spinning jet into acoagulation bath to produce lyocell fibres, and incorporating ananti-microbial composition into the fibres, characterized in that theanti-microbial composition is added to the spinning solution or to aprecursor or ingredient of that solution and comprises a silver compounddeposited on a support material in the form of porous particles havingan extended surface area and comprising an oxidic material which isessentially insoluble in water and incapable of forming hydrates.
 12. Aprocess according to claim 11, in which the spinning solution is made byforming a precursor comprising a pre-mix of cellulose pulp and aqueousamine oxide solvent having excess water over the optimum required forsolution to take place, characterized in that the anti-microbialcomposition is added to the pre-mix, and water is then evaporated fromthe pre-mix to form the spinning solution having the anti-microbialagent dispersed therein. 13-14. (canceled)
 15. A process according toclaim 12, wherein the anti-microbial composition is added in the form ofa dispersion in a liquid.
 16. A process according to claim 15, whereinthe lyocell fibres are subjected to one or more treatments comprisingscouring or washing to substantially remove any residual colourationformed during the fibre-making process.
 17. A process according to claim11, wherein the anti-microbial composition is added in the form of adispersion in a liquid.
 18. A process according to claim 11, wherein thelyocell fibres are subjected to one or more treatments comprisingscouring or washing to substantially remove any residual colourationformed during the fibre-making process.
 19. Anti-microbial lyocellfibres according to claim 1, wherein the porous particles comprising theoxidic support material have an average particle diameter below 25microns.
 20. Anti-microbial lyocell fibres according to claim 19,wherein the porous particles have a surface area in the range 1 to 240square metres per gram.
 21. Anti-microbial lyocell fibres according toclaim 1, wherein the porous particles have a surface area in the range 1to 240 square metres per gram.
 22. Anti-microbial lyocell fibresaccording to claim 1, wherein the silver compound has a low solubilityin water and has silver present as an ionic species.
 23. Anti-microbiallyocell fibres according to claim 22, wherein the silver compound is ata level of concentration of 1 to 75 percent by weight of the oxidicsupport material.
 24. Anti-microbial lyocell fibres according to claim23, wherein the silver compound comprises silver chloride. 25.Anti-microbial lyocell fibres according to claim 1, wherein the silvercompound is at a level of concentration of 1 to 75 percent by weight ofthe oxidic support material.
 26. Anti-microbial lyocell fibres accordingto claim 1, wherein the silver compound comprises silver chloride. 27.Anti-microbial lyocell fibres according to claim 3, wherein the silvercompound comprises silver chloride.
 28. Anti-microbial lyocell fibresaccording to claim 1, wherein the anti-microbial composition is in aconcentration in the fibres of below 1 percent by weight owc. 29.Anti-microbial lyocell fibres according to claim 28, wherein theanti-microbial composition is in a concentration in the fibres of below0.1 percent by weight owc.